Photoelastic Circular Cylinders in Axial Compression

A novel method for fabricating “near-perfect” circular cylinders of photoelastic plastic is presented. The spin-casting technique was found to yield circular cylinders having thickness variations as low as ±0.0006 in., and capable of maintaining this tolerance on shells with radius-to-thickness ratios in the range of 100 ⩽ R/t ⩽ 600. The cylinders generally were found to buckle within 10 per cent of the classical computed load, and within only a few per cent of the reduced value taking into account the clamped end constraints. This represents an increase over previous experimental data. Buckling was completely elastic, and, as a result, repeatability of the buckling load and buckling process was observed for as many as 20 tests on any one shell. Experimental evidence of the unstable states occupied by the shell during the buckling process was found by photographing the change in the 45-deg isoclinics with wave shape. Shell alignment, end constraints, and the method of applying a uniform compressive end load on the cylinder are also discussed. Although no new techniques were employed, the methods used were found reliable and accurate.